The cellular phones of recent years possess a wireless LAN communication function in addition to communication functions that is able to perform a telephone call and data communications via a normal public mobile communications network. Furthermore, these cellular phones are able to perform a telephone call or data communications by connecting to a wireless LAN via an access point. Here, the user holding the cellular phone sometimes moves outside the communication range of the base station when moving while performing a telephone call or data communications using a normal communication function. Here, in cases where it is possible to connect to an access point, performing a call using the wireless LAN via the access point and handover between different so-called communication modes may be considered. For example, NonPatent Document 1 discloses a communication system which comprises a CCCF/NeDS (Call Continuity Control Function/Network Domain Selection) for performing handover between different communication modes in this context.
[NonPatent Document 1] 3GPP “3GPPTR 23.806 V7.0.0(2005-12) 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Voice Call Continuity between CS and IMS Study (Release 7)”, page 40, 6.3.4 Origination, [online], Dec. 25, 2005, Jan. 6, 2006, Internet <URL: http://www.3 gpp.org/ftp/Specs/archive/23_series/23.806/>